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    SubjectRe: [PATCH RESEND 06/16] mfd: add TI LMU driver
    On Wed, 25 Nov 2015, Kim, Milo wrote:

    > On 11/24/2015 5:18 PM, Lee Jones wrote:
    > >On Tue, 24 Nov 2015, Kim, Milo wrote:
    > >
    > >>On 11/24/2015 11:35 AM, Kim, Milo wrote:
    > >>>Hi Lee,
    > >>>
    > >>>Thanks for all your comments. Please see my comments below.
    > >>>
    > >>>On 11/23/2015 7:30 PM, Lee Jones wrote:
    > >>>>>+int ti_lmu_read_byte(struct ti_lmu *lmu, u8 reg, u8 *read)
    > >>>>>>+{
    > >>>>>>+ int ret;
    > >>>>>>+ unsigned int val;
    > >>>>>>+
    > >>>>>>+ ret = regmap_read(lmu->regmap, reg, &val);
    > >>>>>>+ if (ret < 0)
    > >>>>>>+ return ret;
    > >>>>>>+
    > >>>>>>+ *read = (u8)val;
    > >>>>>>+ return 0;
    > >>>>>>+}
    > >>>>>>+EXPORT_SYMBOL_GPL(ti_lmu_read_byte);
    > >>>>It doesn't get much more simple than this.
    > >>>>
    > >>>>What's the purpose of abstracting it?
    > >>>>
    > >>>>>>+int ti_lmu_write_byte(struct ti_lmu *lmu, u8 reg, u8 data)
    > >>>>>>+{
    > >>>>>>+ return regmap_write(lmu->regmap, reg, data);
    > >>>>>>+}
    > >>>>>>+EXPORT_SYMBOL_GPL(ti_lmu_write_byte);
    > >>>>>>+
    > >>>>>>+int ti_lmu_update_bits(struct ti_lmu *lmu, u8 reg, u8 mask, u8 data)
    > >>>>>>+{
    > >>>>>>+ return regmap_update_bits(lmu->regmap, reg, mask, data);
    > >>>>>>+}
    > >>>>>>+EXPORT_SYMBOL_GPL(ti_lmu_update_bits);
    > >>>>Okay, I lied, it does get more simple.
    > >>>>
    > >>>>Seems like abstraction for the sake of abstraction here.
    > >>>>
    > >>>>Feel free to try and convince me otherwise.
    > >>>>
    > >>>
    > >>>The main reason was that LMU MFD core provides consistent register
    > >>>access among LMU drivers like ti-lmu-backlight, leds-lm3633,
    > >>>lm363x-regulator and ti-lmu-fault-monitor('ti-lmu-hwmon' will be changed
    > >>>to this in the 2nd patch).
    > >>>
    > >>>However, LMU register helpers are exactly same as regmap interface
    > >>>except using ti_lmu data structure. So let me replace them with regmap
    > >>>functions. Thanks for pointing this out.
    > >>
    > >>I just realized LMU MFD core helpers also provide module
    > >>dependencies by using EXPORT_SYMBOL_GPL().
    > >>
    > >># modprobe -D ti-lmu-backlight
    > >>insmod /lib/modules/<ver>/kernel/drivers/base/regmap/regmap-i2c.ko
    > >>insmod /lib/modules/<ver>/kernel/drivers/mfd/mfd-core.ko
    > >>insmod /lib/modules/<ver>/kernel/drivers/mfd/ti-lmu.ko
    > >>insmod /lib/modules/<ver>/kernel/drivers/video/backlight/ti-lmu-backlight.ko
    > >># modprobe -D ti-lmu-fault-monitor
    > >>insmod /lib/modules/<ver>/kernel/drivers/base/regmap/regmap-i2c.ko
    > >>insmod /lib/modules/<ver>/kernel/drivers/mfd/mfd-core.ko
    > >>insmod /lib/modules/<ver>/kernel/drivers/mfd/ti-lmu.ko
    > >>insmod /lib/modules/<ver>/kernel/drivers/mfd/ti-lmu-fault-monitor.ko
    > >># modprobe -D lm363x-regulator
    > >>insmod /lib/modules/<ver>/kernel/drivers/base/regmap/regmap-i2c.ko
    > >>insmod /lib/modules/<ver>/kernel/drivers/mfd/mfd-core.ko
    > >>insmod /lib/modules/<ver>/kernel/drivers/mfd/ti-lmu.ko
    > >>insmod /lib/modules/<ver>/kernel/drivers/regulator/lm363x-regulator.ko
    > >># modprobe -D leds-lm3633
    > >>insmod /lib/modules/<ver>/kernel/drivers/base/regmap/regmap-i2c.ko
    > >>insmod /lib/modules/<ver>/kernel/drivers/mfd/mfd-core.ko
    > >>insmod /lib/modules/<ver>/kernel/drivers/mfd/ti-lmu.ko
    > >>insmod /lib/modules/<ver>/kernel/drivers/leds/leds-lm3633.ko
    > >>
    > >>ti-lmu.ko should be loaded first because it has hardware enable pin
    > >>control code. Four other drivers have dependency on this module.
    > >>Without EXPORT_SYMBOL_GPL(), this dependency will be gone like
    > >>below.
    > >>
    > >># modprobe -D ti-lmu-backlight
    > >>insmod /lib/modules/<ver>/kernel/drivers/video/backlight/ti-lmu-backlight.ko
    > >># modprobe -D ti-lmu-fault-monitor
    > >>insmod /lib/modules/<ver>/kernel/drivers/mfd/ti-lmu-fault-monitor.ko
    > >># modprobe -D lm363x-regulator
    > >>insmod /lib/modules/<ver>/kernel/drivers/regulator/lm363x-regulator.ko
    > >># modprobe -D leds-lm3633
    > >>insmod /lib/modules/<ver>/kernel/drivers/leds/leds-lm3633.ko
    > >>
    > >>If LMU MFD core module is not loaded and other modules call regmap
    > >>helpers, then loaded drivers will not work because hardware is not
    > >>enabled yet.
    > >>
    > >>So I'd like to keep LMU MFD helpers for module dependencies.
    > >>Additionally, I'll modify 'ti_lmu_read_byte()' as follows.
    > >>
    > >>int ti_lmu_read_byte(struct ti_lmu *lmu, u8 reg, u8 *read)
    > >>{
    > >> return regmap_read(lmu->regmap, reg, (unsigned int *)read);
    > >>}
    > >>EXPORT_SYMBOL_GPL(ti_lmu_read_byte);
    > >>
    > >>Please let me know if you have better idea.
    > >
    > >You're keeping the helpers for the wrong reasons. This has now become
    > >a hack. If you have dependencies between modules, either use the init
    > >levels or defer probe in the usual way.
    > >
    >
    > Yes, I was wrong. In case LMU MFD core is not loaded, other LMU
    > modules like ti-lmu-backlight isn't probed because no platform
    > device (mfd device) exists. So the situation which I've mentioned
    > never happens.
    > And if GPIO controller is not ready and HW enable GPIO request gets
    > failed on LMU MFD initialization, this will be processed later
    > because it returns as error code '-EPROBE_DEFER' from GPIO
    > subsystem. In other words, there is no dependency issue between LMU
    > modules. Those are just platform device and driver.
    >
    > OK, I'll remove LMU register helpers in the 2nd patch. Then, each
    > LMU driver will call regmap helpers directly.
    > Thanks for your comments.

    No problem. You are welcome.

    --
    Lee Jones
    Linaro STMicroelectronics Landing Team Lead
    Linaro.org │ Open source software for ARM SoCs
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